System and method for detecting display disconnection

ABSTRACT

A video processing device comprises a display interface coupleable to a display device and a display controller configured to transmit a video signal via an output node of the display interface. The video signal comprises an active segment comprising video information and an inactive segment comprising synchronization information. The video processing device further comprises a display detector configured to determine whether the display device is coupled to the display interface based on a comparison of a first voltage at the output node during transmission of the inactive segment to a second voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. provisional applicationSer. No. 61/033,680 filed on Mar. 4, 2008 and entitled “System andMethod for Detecting Display Disconnection”, the entirety of which isincorporated by reference herein.

The present application is related to co-pending U.S. non-provisionalapplication Ser. No. 12/270 384 filed on even date herewith and entitled“System and Method for Detecting Accessory Connection and AccessoryClass”, the entirety of which is incorporated by reference herein.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to interfacing to a displaydevice or other accessory device and more specifically to detectingwhether a display device or other accessory device is connected.

BACKGROUND

Many components of a video processing system, such as a televisionencoder or a video digital-to-analog converter, consume a relativelyhigh amount of power while activated. It therefore can be advantageousto detect when a display device has been disconnected so that the videoprocessing system can enter a low power state. Moreover, a user maydesire to exchange one display device for another (e.g., swappingbetween a monitor and a projector device) and therefore it typically isdesirable to detect the swapping of display devices so that the displaysystem can reinitialize its display configuration for the new displaydevice. Certain display interface architectures, such as those based onthe Digital Video Interface (DVI) specifications, utilize an interfacepin dedicated to detecting a connection between a video processingdevice and a display device. However, other display architectures, suchas those based on the video graphics array (VGA) specifications,composite video specifications, component video specifications, and thelike, do not have a dedicated pin or line for detecting a connectionwith a display device. A conventional technique for detecting aconnection with a display device without a dedicated detection interfacepin includes indiscriminately driving a fixed current at an output lineof the display interface of the video processing device under softwarecontrol or in response to user input, and then measuring the voltage atthe output line to determine whether a display device is connected.While this fixed current often is chosen to be output at the lastdisplay line of a frame, this resulting fixed pattern remains viewableand therefore corrupts the displayed imagery, which can cause visualartifacts bothersome and distracting to the viewer. Moreover, thesoftware intervention and control needed to implement the detectionprocess typically results in a decrease in overall performance and anincrease in power consumed. Accordingly, an improved technique fordetecting whether a display device is connected would be advantageous.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art byreferencing the accompanying drawings. The use of the same referencesymbols in different drawings indicates similar or identical items.

FIG. 1 is a block diagram illustrating an information handling systemincluding components to detect a connection or disconnection of adisplay device in accordance with at least one embodiment of the presentdisclosure.

FIG. 2 is a state diagram illustrating an example method for automaticdisplay device connect/disconnect detection in accordance with at leastone embodiment of the present disclosure.

FIG. 3 is a diagram illustrating an example implementation of a displaycontroller of the information handling system of FIG. 1 in accordancewith at least one embodiment of the present disclosure.

FIG. 4 is a flow diagram illustrating an example method for detecting adisconnection of a display device from a video processing device in thecontext of the implementation of FIG. 3 in accordance with at least oneembodiment of the present disclosure.

FIG. 5 is a flow diagram illustrating an example method for detecting aconnection of a display device to a video processing device in thecontext of the display controller implementation of FIG. 3 in accordancewith at least one embodiment of the present disclosure.

FIG. 6 is a diagram illustrating another example implementation of adisplay controller of the information handling system of FIG. 1 inaccordance with at least one embodiment of the present disclosure.

FIG. 7 is a flow diagram illustrating an example method for detecting adisconnection of a display device from a video processing device in thecontext of the display controller implementation of FIG. 6 in accordancewith at least one embodiment of the present disclosure.

FIG. 8 is a timing diagram illustrating an example operation of thedisplay controller implementation of FIG. 6 in accordance with at leastone embodiment of the present disclosure.

FIG. 9 is a diagram illustrating display modes associated with ahorizontal trace time and a vertical trace time of a signal provided toa display device in accordance with at least one embodiment of thepresent disclosure.

FIG. 10 is a diagram illustrating yet another example implementation ofa display controller of the information handling system of FIG. 1 inaccordance with at least one embodiment of the present disclosure.

FIG. 11 is a flow diagram illustrating an example method for detecting adisconnection of a display device from a video processing device in thecontext of the display controller implementation of FIG. 10 inaccordance with at least one embodiment of the present disclosure.

FIG. 12 is a diagram illustrating an additional example implementationof the display controller of the information handling system of FIG. 1in accordance with at least one embodiment of the present disclosure.

FIG. 13 is a flow diagram illustrating an example method for detectingwhether an accessory is connected to a video processing device, and ifconnected, an accessory class in the context of the display controllerimplementation of FIG. 12 in accordance with at least one embodiment ofthe present disclosure.

DETAILED DESCRIPTION OF THE FIGURES

FIGS. 1-13 illustrate example techniques for determining whether adisplay device or other accessory device is connected to a videoprocessing device and configuring the video processing deviceaccordingly. For ease of illustration, various embodiments of theexample techniques of the present disclosure are described in thecontext of a system utilizing a red-green-blue (RGB) color space, whileother embodiments are described in the context of a system utilizing acomposite video signal or s-video signal, such as a National TelevisionStandards Committee (NTSC)-compliant video signal. However, thosetechniques illustrated in the context of the RGB color space also can beimplemented in other color spaces, such as luma-chroma color spaces(e.g., YUV), or in a composite context using the guidelines providedherein without departing from the scope of the present disclosure.Likewise, those techniques illustrated in the context of a compositevideo signal and s-video signal can be implemented based on a componentvideo signal can be implemented in the context of a composite videosignal using the guidelines provided herein without departing from thescope of the present disclosure.

FIG. 1 illustrates an information handling system 100 in accordance withat least one embodiment of the present disclosure. The informationhandling system 100 includes a video processing device 102 forprocessing video data for display at any of a variety of display devicescoupleable to the video processing device 102, for processing audio datafor output at any of a variety of audio accessory devices, or acombination thereof. Examples of the display devices can include atelevision or a computer monitor (represented as display device 104), aprojection display (represented as display device 106), and the like.Audio accessory devices (not shown) can include, for example, an audioreceiver, one or more speakers, headphones, headsets, microphones, andthe like. Examples of the video processing device 102 include a digitalversatile disk (DVD) player, a set-top box or other television receiver,a notebook computer, a desktop computer, a video-enabled cellphone, apersonal digital assistant, a portable audio/video player, and the like.The functions of the components of the information handling system canbe implemented as hardware, firmware, software (that is executed by oneor more processors), or a combination thereof. To illustrate, certaincomponents can be implemented as discrete logic, an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA), andthe like, while other functions of certain components can be implementedbased on software instructions executed by one or more processors of aprocessing system. Further, some or all of the components canimplemented in a processing device designed based on a set ofregister-transfer-level (RTL), Verilog instructions, or other hardwaredescriptor instructions that define the functionality of the processingdevice and which are synthesized to generate the electrical andelectronic design of the processing device.

In the depicted example, the video processing device 102 includes a hostprocessor 108, memory 110, and a display controller 112. The hostprocessor 108 is used to process commands within video processing device102. For example, commands associated with an application stored inmemory 110 can be processed for a user by the host processor 108.Further, the host processor 108 (or a separate component) is used toprocess multimedia data received from a multimedia source, such as aDVD, a satellite transmission, the Internet, and the like. Toillustrate, the multimedia data can be received in an encoded form, suchas data encoded in accordance with a Motion Pictures Experts Group(MPEG) specification, and the host processor 108 or another componentcan include an MPEG decoder to decode the multimedia data into itscorresponding video data and audio data. Alternately, the multimediainformation can be received in an analog form, such as an analogcomposite signal in accordance with the National Television StandardsCommittee (NTSC) specification or the Phase Alternating Line (PAL)specification. In this implementation, the host processor 108, alongwith a tuner and other components, can receive the analog signal, andfilter and process the analog signal to generate digital data forfurther processing at the video processing device 102.

The display controller 112 receives video data to be output for displayand generates the corresponding video signals for controlling a displaydevice that can be connected to the video processing device 102, such asthe display device 104 or the display device 106. In the illustratedembodiment, the display controller 112 includes a video encoder 114, anoutput display interface 116, a display detector 120 and a controller118. The video encoder 114 can include, for example, a televisionencoder that receives the video data and converts or otherwise formatsthe video data consistent with the display format of the display device,such as an NTSC encoder, a PAL encoder, a composite video encoder, acomponent video encoder, etc. The output display interface 116 comprisescomponents to convert the video data into the corresponding electroniccontrol signals for output to a display device. The output displayinterface 116 further includes the receptacle mechanism used tophysically and electrically connect the video processing device 102 to adisplay device or accessory device, either directly or via a cable orother display connector. In one embodiment, a plurality of outputdisplay interfaces 116 are implemented by the video processing device102 so as to be compatible with different connector architectures. Toillustrate, the output display interface 116 can include an RCA jackconnector or coaxial cable connector for composite video signaling, aVGA connector, a 4-pin DIN s-video connector, or RCA connectors forcomponent video signaling, and the like.

In at least one embodiment, the video processing device 102 outputs avideo signal composed of inactive segments and active segments. Theinactive segments carry non-visual information such as synchronizationinformation (e.g., vertical blanking and horizontal blanking),closed-captioning content (which is subsequently converted to visualinformation by a display device), and the like. The active segmentscarry visual information representative of pixels to be displayed on adisplay device (if connected), such as color information, luminanceinformation, chrominance information, and the like. During an inactivecomponent (e.g., a vertical sync component) of some or all of theinactive segments of the video signal result in a relatively fixedpredetermined voltage or current. As discussed in greater detail below,because the output node has a higher overall resistance when a displaydevice is not connected and a lower overall resistance when a displaydevice is connected, and as the video signal is relatively fixed duringthe inactive component, a voltage determined at the output node duringthe output of the inactive component of the video signal can be comparedwith a predetermined reference voltage to determine whether a displaydevice is connected. The use of inactive components of inactive segmentsof a video signal to detect a connection of a display device avoidsdistorting the segments of the video signal associated with pixelcharacteristics (e.g., color, luminance, etc.), and, thus, reduces theamount of corruption or distortion of the displayed imagery detectableby a viewer.

The display detector 120 includes circuitry for detecting whether adisplay device is connected to the output display interface 116. In oneembodiment, the circuitry of the display detector 120 includes ahardware-implemented state machine configured to implement thetechniques described herein. As described in greater detail herein withreference to FIGS. 3 and 4, the display detector 120, in one embodiment,is configured to take advantage of the ability of certain displaydevices to sample and adjust to a non-zero reference black level on theinput video signal so that a fixed offset current can be supplied forthe purposes of detecting a disconnection of a display device withoutincurring visual artifacts in the displayed video content at the displaydevice. As described in greater detail herein with reference to FIG. 5,the display detector 120, in one embodiment, is configured to disableits digital-to-analog converter (DAC) and then drive a fixed current atthe output display interface 116 so as to determine whether a displayhas been connected to the video processing device 102. Further, asdescribed in greater detail with reference to FIGS. 6-9, the displaydetector 120, in one embodiment, is configured to utilize inactivesegments of a video signal output via the output display interface 116to determine whether a display device is connected to the output displayinterface 116. FIGS. 10 and 11, as discussed in detail below, illustrateanother embodiment of the display detector 120 whereby the displaydetector 120 is configured to detect whether a display device has beendisconnected based the output of a sequence of one or more known pixelvalues and comparing the resulting voltage at the output displayinterface to a reference voltage. In the embodiments of FIGS. 12 and 13,the display detector 120 can be configured to detect whether a displaydevice or other accessory device is connected based on the use of one ormore resistors that can be selectively connected to an output node ofthe output display interface 116.

In response to detecting a newly-connected display device, the displaydetector 120 can provide a connect indicator to the controller 118. Inresponse to the connect indicator the controller 118 can determinecertain characteristics of the connected display device, if available,and configure the display controller 112 accordingly. For example, thecontroller 118 can determine the make, model, or type of display deviceconnected to the output display interface 116 if such information isaccessible through additional communication channels with the displaydevice and then load the appropriate device drivers, and, further, candisable any other display connectors and associated circuitry at thevideo processing device 102. Conversely, in response to detecting adisconnection of a display device from the output display interface 116,the display detector 120 can provide a disconnect indicator to thecontroller 118. In response to the disconnect indicator, the controller118 can configure the display controller 112 and other display-relatedcomponents of the video processing device 102 into a low-power state soas to conserve power. To illustrate, the controller 118 can disable thevideo encoder 114 and the components of the output display interface 116while no connection to a display device is detected. Further, thecontroller 118 can disable a tuner or other input that receives andprocesses multimedia data for the video processing device 102, unless itwould otherwise be desirable to preprocess and store the multimedia datawhile waiting for a connection to a display device.

When connected, the display devices 104 and 106 each processes signalsgenerated by display controller 112 for presenting a sequence of images(frames or fields) associated with video processing device 102 to aviewer. The display device 104 includes a display input interface 124compatible with an interface cable 126 or other type of interconnectthat can be used to connect the display input interface 124 with theoutput display interface 116. The display device 106 includes a displayinput interface 128 compatible with an interface cable 130 that can beused to connect the display input interface 128 with the output displayinterface 116.

In one embodiment, the terminal resistances of some or all of the signallines of the output display interface 116, the display input interfaces124, or the display input interface 128 are substantially equal to aknown, or prescribed, terminal resistance (e.g., 75Ω) and variousaccessory classes of accessory devices potentially connected to thevideo processing device 102 may have their own known terminalresistances. Accordingly, when the output display interface 116 is notconnected to a display device, the effective terminal resistance at thesignal line or pin (hereinafter referred to as an “output node”) of theoutput display interface 116 is equal to the terminal resistance of thenode of the output display interface 116 itself (e.g., 75Ω). However,when the output display interface 116 is connected to a display devicevia an interface cable or other connector, the effective terminalresistance at the node of the output display interface 116 is equal tothe terminal resistance of the node of the output display interface 116and the corresponding node of the display input interface in parallel(e.g., 37.5Ω or 75Ω∥75Ω). Thus, given a fixed current provided at theoutput node of the output display interface 116, the output node willhave a higher voltage when the output display interface 116 is notconnected to a display device than when the output display interface 116is connected to a display device.

As described in greater detail herein, the display detector 120 uses thedifferent possible terminal resistances of the output node to determinewhether a display device or other accessory device is connected, and insome implementations, what class of accessory is connected. The resultthen can be used to set either the connect indicator or the disconnectindicator as described above. In the event that a disconnection of adisplay device is detected, the controller 118 can disable one or moredisplay-related components of the video processing device 102 so as toconserve power.

Referring to FIG. 2, a state diagram 200 is illustrated in accordancewith at least one embodiment of the present disclosure. For ease ofdiscussion, the state diagram 200 is described in the example context ofthe information handling system 100 of FIG. 1. The state diagram 200 canbe implemented as software, firmware, hardware, or a combinationthereof. To illustrate, the state diagram 200 can be implemented as ahardware state machine by the display detector 120, the controller 118,or a combination thereof. By implementing a hardware state machine tocontrol the display device connect/disconnect state,performance-degrading and power-sapping intervention by software can bereduced or eliminated.

In response to a start-up or reset stimulus, the state diagram 200enters state 202 whereby the video processing device 102 is initialized.As part of the initialization process, the display controller 112 can beconfigured into a default mode whereby the display controller 112 isconfigured to operate with a default set of display devices. Wheninitialization is completed, the state diagram 200 enters state 204. Atstate 204 the video processing device 102 determines whether a displaydevice is connected to the output display interface 116. Exampletechniques for detecting the connection of a display device or otheraccessory device to the video processing device 102 are described belowwith reference to FIGS. 5, 12, and 13. In the event that a connection isnot detected, the state machine 200 enters state 206. At state 206, thecontroller 118 configures display-related components of the videoprocessing device 102 into a low power state, such as by disabling thevideo encoder 114 and a video DAC of the output display interface 116.When the configuration of the low power mode is completed, the statediagram 200 returns to state 204.

In the event that a connection to a display device or other accessorydevice is detected at state 204, the display detector 120 generates theconnect indicator and the state diagram 200 enters state 208. At state208 the controller 118 can determine the characteristics of theconnected display device, if available, and configures the displaycontroller 112 accordingly. This configuration can include enablingpreviously-disabled components, loading device drivers, and the like.When the configuration has completed, the state diagram 200 enters state210. At state 210 the display detector 120 determines whether thedisplay device has been disconnected. Example techniques for detectingthe disconnection of a display device or other accessory device aredescribed below with reference to FIGS. 4, 7, 8, 11, and 13. In theevent that a disconnection is detected, the display detector 120generates the disconnect indicator and the state diagram 200 reentersstate 206.

FIG. 3 illustrates an example implementation of the display controller112 of FIG. 1 in conjunction with an input display interface 302 of adisplay device and a cable interface 304 in accordance with oneembodiment of the present disclosure. In the example of FIG. 3, theoutput display interface 116 is utilized to provide component-type videoto the display device, such as video signaling based on a Red-Green-Blue(RGB) color space. Accordingly, the output display interface 116includes a video DAC 306 configured to convert digital pixel values,such as digital pixel streams RED_IN, GREEN_IN, and BLUE_IN(corresponding to the red, green, and blue color component informationrespectively), to corresponding representative electronic signalstransmitted to the input display interface 302 over differentcorresponding lines of the cable interface 304. In at least oneembodiment, the video DAC 306 is a current-steering DAC that generates acurrent for output that varies with the pixel values of thecorresponding input signal.

In the example of FIG. 3, the display detector 120 includes aconnect/disconnect detect module 310, an offset current generator 312, areference voltage generator 314, a comparator 316, and an output latch318. The connect/disconnect detect module 310 comprises logic and othercircuitry configured to provide an enable indicator or enable signal(ENABLE) for latching a DISPLAY_DET signal at the output latch 318 and adisable indicator or disable signal (DISABLE) for disabling at least thevideo DAC 306.

In operation, the offset current generator 312 provides a fixed offsetcurrent I_(OFFSET) to the output node of the output display interface116 corresponding to a particular color component (e.g., the red colorcomponent in the example of FIG. 3) during the transmission of one ormore frames of video content (including the inactive segments of thevideo signal such as the horizontal sync (hsync) and vertical sync(vsync) segments) to the input display interface 302 of the displaydevice. The offset current I_(OFFSET) is combined with the currentI_(RED) generated by the video DAC for the red color component resultingin the generation of a combined current I_(RED′)(I_(RED′)=I_(RED)+I_(OFFSET)) that results in a corresponding voltageV_(RED) at the corresponding input node of the input display interface302 of the display device. As the current sourced by the video DAC 306during certain inactive segments of the video signal typically is closeto zero (I_(RED)(inactive)=0), the combined current I_(RED′) typicallyis approximately equal to the offset current I_(OFFSET)(I_(RED′)(inactive)=I_(OFFSET)).

The output of the current I_(RED′) at the selected output node resultsin a voltage V_(RED) at the output node that is based on the effectiveterminal resistance R_(NODE) at the output node. In the event that thedisplay device is not connected, the effective terminal resistance issubstantially equal to the terminal resistance of the output displayinterface 116 at the output node (identified as resistance R_(HR) inFIG. 3), that is, R_(NODE)=R_(HR), and thus the voltage V_(RED) is equalto I_(RED′)*R_(HR). In contrast, when the display device is connected,the effective terminal resistance is substantially equal to theresistance R_(HR) of the video processing device 102 with respect to theoutput node and the resistance of the display device (identified asresistance R_(DR) in FIG. 3) with respect to the output node inparallel; that is R_(NODE)=R_(HR)∥R_(DR) (where R_(HR)∥R_(DR)<R_(HR)),and thus the voltage V_(RED) is equal to I_(RED′)* (R_(HR)∥R_(DR)).

In at least one embodiment, the display device includes a monitor orother display device configured to sample the reference black level ofan input signal by determining the voltage present on input nodes of theinput display interface 302 during inactive segments of the receivedvideo signal and to readjust the black level with a corresponding offsetvoltage using any of a variety of well-known techniques. Accordingly, asthe offset current I_(OFFSET) is the only substantial source of currentat the output node associated with the red component, and thus thesource of the voltage at the input line for the red component of thevideo signal during the initial inactive segments, the display devicesamples the voltage (V_(OFFSET)) resulting from the offset currentI_(OFFSET) as reference black so that the offset current I_(OFFSET) doesnot affect the image displayed when it is provided in conjunction withthe current I_(RED) during the active periods of the video signal, eventhough the offset current I_(OFFSET) is present in the output currentI_(RED′) during the active segments. It will be appreciated that certaintypes of display devices may not be capable of sampling the offsetvoltage V_(OFFSET) present during the inactive segments of the videosignal as the reference black level and thus the presence of the offsetcurrent I_(OFFSET) may affect the display of the video content in theseinstances. To illustrate, the Video Electronics Standards Association(VESA) Video Signal Standard (VSIS) provides that the RGB values duringinactive segments must be at 0.0 Volts (V), and thus monitors compliantwith the VESA VSIS standard typically are not required to be configuredto sample the offset voltage V_(OFFSET) during the inactive segments asthe reference black level for the active segments so that the presenceof the offset current I_(OFFSET) in the output current I_(RED′) duringthe active segments would have the potential to affect the display ofvideo content during the active segments.

Based on the different levels of V_(RED) resulting from the provision ofthe offset current V_(OFFSET) to the output node during an inactivesegment of the video signal and based on the ability of the displaydevice to compensate for the presence of the offset current I_(OFFSET),the display detector 120 can determine whether the display device hasbeen disconnected from the output display interface 116. The comparator316 compares the voltage V_(RED) at the output node during the inactivesegment with a reference voltage V_(REF) output by the reference voltagegenerator 314, wherein the reference voltage V_(REF) is between thevoltage level at the output node expected in the event that a displaydevice is connected and the voltage at the output node expected in theevent that a display device is not connected. When an inactive segment(e.g., an hsync or vsync component) that is to serve as the impetus forthe detection process is being transmitted via the output node, theconnect/disconnect detect module 310 provides the enable indicator sothat the output latch 318 latches the output of the comparator 316 atthe time of the transmission of the inactive segment, whereby the outputof the comparator 316 at this time represents the comparison of thevoltage V_(RED) of the output node at the time of transmission of theinactive segment to the voltage reference V_(REF). Thus, in the eventthat the voltage V_(RED) is greater than the reference voltage V_(REF)(and thus no display device is connected) during the transmission of theinactive segment, the comparator 316 configures its output to a firstvalue (e.g., zero), which is latched by the output latch 318 in responseto the enable indicator. In the event that the voltage V_(RED) is lessthan the reference voltage V_(REF) (and thus a display device isconnected) during the transmission of the inactive segment, thecomparator 316 configures its output to a second value (e.g., one),which is latched by the output latch 318 in response to the enableindicator. The output of the output latch 318 is provided as a displaydetect signal (DISPLAY_DET), whereby the DISPLAY_DET signal having thefirst value and the DISPLAY_DET signal having the second value can serveas the connect indicator and disconnect indicator, respectively,provided to the controller 118 as described above. In the event that theDISPLAY_DET signal is unasserted, or zero, the display device isidentified as having been disconnected from the video processing device102 and thus the connect/disconnect detect module 310 can provide thedisable indicator so as to disable the video DAC 306 and otherdisplay-related components of the video processing device 102 for atleast a predetermined period.

FIG. 4 illustrates an example method 400 for determining whether adisplay device has been disconnected from a video processing device inaccordance with at least one embodiment of the present disclosure. Forease of discussion, the method 400 is described in the context ofdisplay controller implementation of FIG. 3. The method 400 canrepresent the operation of the state machine 200 of FIG. 2 for the state210.

At block 402, the video processing device 102 processes video data andoutputs one or more corresponding video signals via the output displayinterface 116. At least one output current representing a correspondingcomponent of the video signal is augmented at the corresponding outputnode with the offset current I_(OFFSET) from the offset currentgenerator 312 during the transmission of one or more frames of videocontent. At block 404, the display device samples the offset voltageV_(OFFSET) present during the inactive segments of the video signal (andgenerated via the offset current I_(OFFSET)) as the reference blacklevel. At block 406, the connect/disconnect detect module 310 monitorsthe video signal to determine whether there is an upcoming inactivesegment of the video signal. In the event that no upcoming inactivesegment is detected at block 408, the method 400 returns to block 406 tocontinue monitoring the video signal. Otherwise, if an upcomingpredetermined inactive segment is detected in the video signal (e.g., apreselected vertical synchronization component or horizontalsynchronization component), the method 400 continues to block 410. Atblock 410, the display detector 120 determines the voltage at the outputnode during the predetermined inactive segment (V_(NODE)(inactive)),where the voltage at the output node during the inactive segment isdependent on the offset current I_(OFFSET) and the effective resistanceat the output node (R_(NODE)), that is: V_(NODE)(inactive)=I_(OFFSET)*R_(NODE). As discussed above, the effectiveresistance at the output node is lower when a display device(hereinafter, resistance R_(C)) is connected than the effectiveresistance at the output node when a display device is not connected(hereinafter, resistance R_(D)). Accordingly, at block 412 thecomparator 316 compares the voltage V_(NODE) (inactive) with a referencevoltage V_(REF), wherein the reference voltage V_(REF) is selected so asto between the voltage V_(C) expected when a display device is connected(V_(C)=I_(OFFSET)*R_(C)) and the voltage V_(D) expected when a displaydevice is not connected (V_(D)=I_(OFFSET)*R_(D)), that is:V_(C)<V_(REF)<V_(D). In the event that the voltage V_(NODE)(inactive) isdetermined to be less than the reference voltage V_(REF) at block 412,the display detector 120 determines that a display device is connectedand therefore generates the connect indicator (e.g., DISPLAY_DET=1) forthe controller 118 at block 414 as described above. The method 400 thenreturns to the block 406 whereupon the process can be repeated foranother detection cycle. In the event that the voltageV_(NODE)(inactive) is determined to be greater than the referencevoltage V_(REF) at block 412, the display detector 120 determines that adisplay device is not connected at block 416 and therefore notifies thedisplay controller 112 by generating the disconnect indicator (e.g.,DISPLAY_DET=0) for the controller 118 as described above. The disconnectindicator can include, for example, an interrupt to be processed by thehost processor 108 of the video processing device 102.

FIG. 5 illustrates an example method 500 for determining whether adisplay device has been connected to, or disconnected from, a videoprocessing device in accordance with at least one embodiment of thepresent disclosure. For ease of discussion, the method 500 is describedin the context of display controller implementation of FIG. 3. Themethod 500 can represent the operation of the state machine 200 of FIG.2 for the state 204.

At block 502, the connect/disconnect detect module 310 disables thevideo DAC 306 as well as other display-related components. At block 504the connect/disconnect detect module 310 configures the voltagegenerator 314 to output a reference voltage V_(REF) related to theoffset current I_(OFFSET) and the node resistances when a display deviceis connected or disconnected as described above. At block 506, theconnect/disconnect detect module 310 enables the offset currentgenerator 312 (if previously disabled) so as to drive the offset currentI_(OFFSET) to the output node of the corresponding color component ofthe video signal. Accordingly, a voltage V_(NODE) results from theconductance of the offset current I_(OFFSET) through the node resistanceR_(NODE) of the output node, where the node resistance is higher if adisplay device is not connected and lower if a display device isconnected. At block 508 the comparator 312 compares the voltage V_(NODE)with the reference voltage V_(REF). In the event that it is determinedat block 510 that the voltage V_(NODE) is less than the referencevoltage V_(REF), the display detector 120 determines that a displaydevice has been connected at block 512 and therefore notifies thedisplay controller 112 by generating the connect indicator (e.g.,DISPLAY_DET=1).

Otherwise, the display detector 120 determines that a display device hasnot been connected at block 516 and therefore maintains or provides thedisconnect indicator. Further, to conserve power in between iterationsof the display connection process, at block 518, the connect/disconnectdetect module disables the offset current generator 312, if not alreadydisabled, and at block 520 the display detector 120 maintains the offsetcurrent generator 312 in a disabled state for a predetermined duration(e.g., 1 second). The predetermined duration can be hardwired, or thepredetermined duration can be programmed via, for example, a valuestored to a particular memory location or register or via a resistor,jumper, or fuse. Further, the predetermined duration can be incremented,decremented, or otherwise adjusted between iterations. After thepredetermined duration has lapsed, the method 500 returns to block 506to repeat the process for the next detection cycle.

FIG. 6 illustrates another example implementation of the displaycontroller 112 of FIG. 1 in conjunction with an input display interface602 of a display device 620 and a cable interface 604 in accordance withone embodiment of the present disclosure. In the example of FIG. 6, theoutput display interface 116 is utilized to provide a composite-typevideo to the display device 620. The output display interface 116includes a video DAC 606 configured to convert the composite digitalvideo signals into a representative analog signal transmitted to theinput display interface 602 over a corresponding line of the cableinterface 604. In at least one embodiment the video DAC 606 is acurrent-steering DAC that generates a current for output that varieswith the digital values of the corresponding input signal.

In the example of FIG. 6, the display detector 120 includes aconnect/disconnect detect module 610 (corresponding to theconnect/disconnect detect module 310 of FIG. 3), a reference voltagegenerator 614 (corresponding to the reference voltage generator 314 ofFIG. 3), a comparator 616 (corresponding to the comparator 316 of FIG.3), and an output latch 618 (corresponding to output latch 318 of FIG.3). The connect/disconnect detect module 610 monitors the operation ofthe output display interface 116 to identify an upcoming inactivesegment of the video signal output by the video DAC 606 withpredetermined voltage/current characteristics. In response to detectingan upcoming inactive segment, the connect/disconnect detect module 610provides an enable indicator.

A current generated by the video DAC 606 for the inactive component(I_(INACTIVE)) is transmitted to the corresponding input node of theinput display interface 602 of the display device 620 during thetransmission of the inactive component, which results in a voltageV_(NODE) at the output node that is based on the effective terminalresistance (R_(NODE)) at the output node. In the event that the displaydevice 620 is not connected, the effective terminal resistance issubstantially equal to the terminal resistance of the output displayinterface 116 at the output node (identified as resistance R_(H) in FIG.6) and thus the voltage V_(NODE) is equal to I_(INACTIVE)*R_(H). Incontrast, when the display device 620 is connected, the effectiveterminal resistance is substantially equal to the resistance R_(H) ofthe video processing device 102 with respect to the output node and theresistance of the display device 620 (identified as resistance R_(D) inFIG. 6) with respect to the output node in parallel, that isR_(NODE)=R_(H)∥R_(D) (where R_(H)∥R_(D)<R_(H)), and thus the voltageV_(NODE) is equal to I_(INACTIVE)* (R_(H)∥R_(D)).

In response to the enable indicator, the comparator 616 compares thevoltage at the selected output node (voltage V_(NODE)) with a referencevoltage V_(REF) output by the reference voltage generator 614. In theevent that the voltage V_(NODE) is greater than the reference voltageV_(REF) (and thus no display device is connected), the comparator 616configures its output to a first value (e.g., zero), which is latched bythe output latch 618 in response to the enable indicator. In the eventthat the voltage V_(NODE) is less than the reference voltage V_(REF)(and thus a display device is connected), the comparator 616 configuresits output to a second value (e.g., one), which is latched by the outputlatch 618 in response to the enable indicator. The output of the outputlatch 618 is provided as the DISPLAY_DET signal and provided to thecontroller 118 as described above.

FIG. 7 illustrates an example method 700 for determining whether adisplay device has been connected to a video processing device inaccordance with at least one embodiment of the present disclosure. Forease of discussion, the method 700 is described in the context ofdisplay controller implementation of FIG. 6. The method 700 canrepresent the operation of the state machine 200 of FIG. 2 for the state210.

At block 702, the connect/disconnect detect module 610 monitors thevideo signal to identify an upcoming inactive segment, such as a vsynccomponent or an hsync component. In the event that the inactive segmentis not yet detected at block 704, the method 700 returns to block 702.Otherwise, if the inactive segment is detected in the video signal, atblock 706 the video DAC 606 drives a predetermined current I_(INACTIVE)representative of at least a portion of the inactive segment to theoutput node, thereby generating a voltage V_(NODE) at the output nodeduring the transmission of the inactive segment. Further at block 706,the connect/disconnect detect module 610 provides the enable indicator.At block 706, the comparator 616 compares the voltage V_(NODE) with areference voltage V_(REF), wherein the reference voltage V_(REF) isselected so as to between the voltage V_(C) expected when a displaydevice is connected (V_(C)=I_(INACTIVE)*R_(C)) and the voltage V_(D)expected when a display device is not connected(V_(D)=I_(INACTIVE)*R_(D)), that is: V_(C)<V_(REF)<V_(D). In the eventthat it is determined at block 710 that the voltage V_(NODE) is lessthan the reference voltage V_(REF), the display detector 120 determinesthat a display device remains connected at block 712, whereupon themethod 700 can return to block 702 to repeat the process for the nextdetection cycle. Otherwise, the display detector 120 determines that adisplay device has been disconnected at block 714 and therefore notifiesthe display controller 714 of the disconnection of the display device atblock 716 by, for example, generating an interrupt or by providing theDISPLAY_DET signal latched at the output latch 618 in response to theenable indicator from the connect/disconnect detect module 610 providedat block 706.

FIG. 8 illustrates an example timing diagram 800 for the video signal(signal 802) output by the video DAC 606 of FIG. 6, the enable indicator(signal 804) output by the connect/disconnect detect module 610, and theDISPLAY_DET indicator (signal 806) output by the output latch 618 ofFIG. 6. The same timing principles can also be applied in theimplementation of FIG. 5.

As illustrated by FIG. 8, the video signal (signal 802) comprises asequence of inactive segments 810 and active segments 812, whereby theinactive segments 810 carry non-pixel information (such as serrationpulses 814 serving as a preamble and vertical sync components 816 and818) and the active segments 812 carry pixel information. In thedepicted example, the connect/disconnect detect module 610 detects theserration pulses 814 and thus determines that a vertical sync componentis upcoming. Once the selected vertical sync component is detected (thevertical sync component 816 in this example), the connect/disconnectdetect module 610 pulses the enable indicator at time t₀, therebyenabling the comparator 616 and other circuitry of the display detector120. By time t₂ the comparator 616 has compared the voltage at theoutput node generated from the fixed current output based on the voltageof the vertical sync component 816 and determined whether the voltage atthe output node is greater than or less than the reference voltageV_(REF). The comparator 616 configures its output accordingly and theconfigured output is reflected by the state of the DISPLAY_DET signal attime t₂.

FIG. 9 is a diagram illustrating portions of time associated with adisplay of a single frame on a display device in accordance with atleast one embodiment of the present disclosure. Time identified fromleft to right indicates an amount of time for a single horizontal trace(horizontal trace time 935). Time indicated from top to bottom indicatesan amount of time to complete a vertical trace (vertical trace time930). It should be noted that a single vertical trace time 930 iscomposed of multiple horizontal trace times 935. A portion of timeindicated by horizontal sync time 940 indicates time used fortransmission of a horizontal sync component to a display device. Thehorizontal sync component indicates a new horizontal trace is to begin.After receipt of the horizontal sync component, the external displaydevice prepares to draw a new horizontal line on the screen. The amountof time indicated by the horizontal back porch time 942 indicates timebefore an active video portion is to be displayed (as indicated byactive display time 960). The active display time 960 is representativeof an image to be displayed. Similarly, the horizontal front porch time944 indicates the portion of time devoted to a horizontal trace afterthe active display portion has been completed.

The vertical sync time 950 indicates a portion of the vertical time inwhich a vertical synchronization component is sent to the externaldisplay device. Upon receipt of the vertical synchronization component,the display device prepares to display a new horizontal line at the topof the screen. The vertical back porch time 952 indicates a portion oftime in which horizontal lines are drawn before horizontal lines whichinclude the active display portion are received. Similarly, the verticalfront porch time 954 includes a portion of time in which horizontallines are drawn after horizontal lines no longer include an activedisplay portion.

As previously discussed, the present disclosure includes providing fixedcurrent to the video signals output to the display device to assist inthe detection of a connection and disconnection of the external displaydevice. To avoid corruption of pixel information made visible to a user,in one embodiment the provision of the fixed current and the detectionof the voltage at the output node of the output display interface isperformed only during an inactive component of the video signal. Toillustrate, the provision of the fixed current for display devicedetection purposes can occur during any of the porch times 942, 944,952, 954, during any of the vertical sync time 950, the horizontal synctime 940, or a combination thereof. It should be noted that portions ofthe vertical back porch time 952, the vertical front porch time 954, thehorizontal back porch time 942, and the horizontal front porch time 944can be displayed on the screen associated with the display device.However, portions of the vertical porches 952 and 954 and the horizontalporches 942 and 944 are generally displayed in black. Accordingly, inthis instance the display detection technique described herein can belimited to the sync times 940 and 950 and the black portion of the porchtimes 942, 944, 952, and 954 so as to reduce visible artifacts duringthe detection process.

FIG. 10 illustrates an example implementation of the display controller112 of FIG. 1 in conjunction with an input display interface 1002 of adisplay device 1003 and a cable interface 1004 in accordance with oneembodiment of the present disclosure. In the example of FIG. 10, theoutput display interface 116 is utilized to provide component-type videoto the display device, such as video signaling based on a Red-Green-Blue(RGB) color space. Accordingly, the output display interface 116includes a video DAC 1006 configured to convert digital video signals,such as digital signals RED_IN, GREEN_IN, and BLUE_IN (corresponding tothe red, green, and blue color component information respectively), tocorresponding representative electronic signals transmitted to the inputdisplay interface 1002 over different corresponding lines of the cableinterface 1004. In at least one embodiment, the video DAC 1006 is acurrent-steering DAC that generates a current for output that varieswith the digital pixel values of the corresponding component of thevideo signal.

In the illustrated embodiment, the display detector 120 includes aconnect/disconnect detect module 1010, a reference voltage generator1014, a comparator 1016, and an output latch 1018 as similarly describedabove with respect to FIGS. 3 and 6. The display detector 120 furtherincludes a threshold register 1022, a digital comparator 1024, a counter1026, a delay register 1028, and an inverter 1030. Theconnect/disconnect detect module 1010 comprises logic and othercircuitry configured to provide an enable indicator or signal (ENABLE)for latching a DISPLAY_DET signal at the output latch 1018, a disableindicator or signal (DISABLE) for disabling at least the video DAC 1006,and a voltage configuration indicator or signal (VCONFIG) to configurethe reference voltage V_(REF) output by the voltage generator 1014. Theconnect/disconnect detect module 1010 further can include logic andother circuitry to provide a threshold value for storage in thethreshold register 1022 and a delay value for storage in the delayregister 1028.

In operation, the comparator 1016 compares a voltage V_(BLUE) at theoutput node of the output display interface 116 for the blue componentwith the reference voltage V_(REF) when a compare indicator (CMP) isprovided (e.g., an assertion of a compare signal), and outputs a valuerepresenting the results of the comparison to the output latch 1018,whereupon the output latch 1018 latches the output voltage of thecomparator 1016 as the DISPLAY_DET signal in response to assertion ofthe enable signal by the connect/disconnect detect module 1010. Thedigital comparator 1024 compares the digital pixel values provides asthe BLUE_IN component to the threshold value of the threshold register1022, and when a digital pixel value exceeds the threshold value, thedigital comparator 1024 asserts its output.

In one embodiment the output of the digital comparator 1024 can serve asthe compare indicator such that when a single digital pixel value isdetected as meeting or exceeding the threshold value, the compareindicator is asserted and the comparator 1016 performs theabove-described comparison. However, as discussed in greater detailbelow, to allow the output current of the video DAC 1006 to settle, inanother embodiment, the counter 1026 is used to ensure that a minimumuninterrupted sequence of digital pixel values greater than thethreshold value occur in the BLUE_IN component before the comparison isinitiated. In this case, the counter 1026 is loaded with the delay value(which represents the minimum number of display values in the sequence)as the initial counter value and then the counter 1026 decrements thecounter value for each digital pixel value that meets or exceeds thethreshold value (as determined by the digital comparator 1024). When thecounter value reaches zero, the counter 1026 then asserts the compareindicator to direct the comparator 1016 to initiate the comparisonprocess. To ensure that the sequence of digital pixel values that meetor exceed the threshold value is contiguous, the inverter 1030 can beused to reset the counter 1026 whenever a digital pixel value isdetermined to not meet or exceed the threshold value. To illustrate,assuming the delay value is set to 8, the compare indicator would not beasserted until eight digital pixel values that meet or exceed thethreshold value are provided in an uninterrupted sequence in the BLUE_INcomponent. Care may be taken to ensure that the delay value, and thusthe number of digital pixel values in the uninterrupted sequence, isreasonable in the context of the video content expected to be displayed.

As discussed above, the terminal resistance at the output node of eachof the color components differs depending on whether a display device isconnected or disconnected to the output display interface 116. Toillustrate, if the output display interface 116 has an effectiveresistance of 75Ω at each output node and the display device has aneffective resistance of 75Ω for each input node, the output node has aterminal resistance of 75Ω when the display device is disconnected and aterminal resistance of 37.5Ω when the display device is connected.Accordingly, for a given output current, the voltage at an output nodewill be lower when the display device is connected than when the displaydevice is disconnected. The implementation of the display controller 112of FIG. 10 takes advantage of the difference in voltages at the outputnode depending on whether a display device is connected or disconnectedby selecting a reference voltage V_(REF) that is greater than thehighest voltage expected at the output node when the display device 1003is connected but is lower than the highest voltage expected at theoutput node when the display device 1003 is disconnected. Accordingly,when the voltage V_(BLUE) is less than or equal to the reference voltageV_(REF) when the compare indicator is asserted, the DISPLAY_DET signalwould be set to 1, thereby indicating the display device 1003 isconnected. Otherwise, when the voltage V_(BLUE) is greater than thereference voltage V_(REF) when the compare indicator is asserted, theDISPLAY_DET signal would be set to 0, thereby indicating the displaydevice 1003 is disconnected.

To illustrate, assuming that a current range of 0 mA to 18.666 mA forthe video DAC 1006 depending on the output pixel value, the normalvoltage range of the video DAC 1006 would be 0.0 V to 0.7 V for aterminal resistance of 37.5Ω (i.e., when the display device 1003 isconnected) and would be 0.0V to 1.4 V for a terminal resistance of 75Ω(i.e., when the display device 1003 is disconnected). In this example,the reference voltage V_(REF) could be set to, for example, 0.8 V. Inthis case, the reference voltage V_(REF) would only be exceeded when theoutput of the video DAC 1006 is at or greater than 10.666 mA (0.8 V/75Ω)when the display device 1003 is disconnected. Further, the output of10.666 mA would result in a voltage of only 0.4 V when the displaydevice 1003 is connected, and thus would not exceed the referencevoltage of 0.8 V. Assuming the video DAC 1006 is a 10 bit DAC with the 0to 18.666 mA current range, the current per digital step is 18.23uA/step. Accordingly, to output a current of at least 10.666 mA, thedigital pixel value input to the video DAC 1006 would have to be atleast 586 or greater. Allowing a margin for error and noise, a thresholdvalue slightly greater than 586, such as 650 (out of 1023) could beloaded into the threshold register 1022. Accordingly, whenever a digitalpixel value of 650 or greater is supplied in the BLUE_IN component, thedigital comparator 1024 would assert its output, which could thentrigger the comparator 1016 to compare the voltage V_(BLUE) at theoutput node resulting from the supply of the current corresponding tothe digital pixel value to the 0.8 V reference voltage. Alternately, toallow the output of the video DAC 1006 to settle, the counter 1026 canbe used to ensure that an uninterrupted sequence of digital pixel valuesof 650 or greater occurs in the BLUE_IN component before beginning thecomparison process. In this example a digital pixel value of 650 wouldbe converted by the video DAC 1006 to a current of 11.849 mA, whichwould result in a voltage V_(BLUE) of 0.888 V if the display device 1003is disconnected or a voltage V_(BLUE) of 0.444 V if the display device1003 is connected. Thus, in this example the comparison of the voltageV_(BLUE) to the 0.8 V reference voltage for the current output of thevideo DAC 1006 corresponding to a digital pixel value of 650 (or anuninterrupted sequence of such values) would allow the display detector120 to determine whether the display device 1003 is connected ordisconnected.

In an alternate embodiment, rather than employing a maximum expectedvoltage for comparison purposes, different voltage ranges depending onwhether the display device 1003 is connected or disconnected can insteadbe implemented. To illustrate, assuming that the output voltage of thevideo DAC 1006 is in a range of 0.0 V to 0.7 V when the display device1003 is connected, the reference voltage V_(REF) could be set to, forexample, 0.5 V and the digital comparator 1024 could be configured todetect digital pixel values that would result in an output voltage ofapproximately 0.3 V to 0.4 volts when the display device 1003 isconnected and an output voltage of approximately 0.6 V to 0.8 V when thedisplay device 1003 is not connected. When one of these digital pixelvalue (or a set of these digital pixel values) is detected, a comparisonof the voltage at the output node to the 0.5 V reference voltage todetermine whether the display device 1003 is connected or disconnected.

Further, in one embodiment, rather than concluding that the displaydevice 1003 is disconnected based on one indication that the displaydevice 1003 is disconnected, the connect/disconnect detect module 1022could implement a counter (not shown) or other mechanism to ensure thata programmable number of disconnect indications from the comparator 1016occur before asserting the enable signal so as to latch the DISPLAY_DETsignal. Further, rather than utilizing only one component of the videosignal to determine whether the display device 1003 is connected ordisconnected, the display controller 112 could employ the illustratedtechnique for two or more of the components (e.g., for each of the red,green, and blue components) of the video signal and then conclude thatthe display device 1003 is connected or disconnected based on theconnect/disconnect status reported by each component (e.g., either bymajority vote or by unanimous vote).

Although FIG. 10 illustrates an implementation whereby the video signalis separated into different components (e.g., RGB components orluma-chroma components), the implementation may be adapted for analog TVsignals. In this case, the reference voltage V_(REF) would be set at avoltage greater than the maximum expected voltage of the analog TVsignal when the display device 1003 is connected.

FIG. 11 illustrates an example method 1100 for determining whether adisplay device has been disconnected from a video processing device inaccordance with at least one embodiment of the present disclosure. Forease of discussion, the method 1100 is described in the context ofdisplay controller implementation of FIG. 10. The method 1100 canrepresent the operation of the state machine 200 of FIG. 2 for the state210.

At block 1102, the connect/disconnect detect module 1010 initializes thedisplay detector 120 to determine the connection state of the displaydevice 1003 by determining a threshold value and a display value andthen storing them in the threshold register 1022 and the delay register1028, respectively. As discussed above, the threshold value can bedetermined based on a maximum expected voltage at an output node of theoutput display interface 116 when the display device is connected (e.g.,the 0.8 V reference voltage discussed in an example above), or based ona voltage range (e.g., the 0.5 V reference voltage discussed in anexample above). Likewise, the delay value can be selected so as toprovide sufficient settling of the output current of the video DAC 1006.The counter 1026 stores the delay value as its counter value.

At block 1104, the digital comparator 1024 monitors the digital valuesrepresenting the pixel data for the corresponding component (e.g., theBLUE_IN component) and compares the digital values with the thresholdvalue. In the event that the digital comparator 1024 determines that thepixel value is not greater than the threshold value at block 1106, thecounter 1026 is reinitialized and the method 1100 returns to block 1104for the next pixel value. Otherwise, at block 1108, the digitalcomparator 1024 asserts its output and the counter 1026 thereforemodifies its counter value (e.g., decrements its counter value).

At block 1110, the counter 1026 determines whether its counter valueequals a settle value. In instances where the counter 1026 is adecrement counter initialized with the delay value, the settle value canbe zero. Alternately, if the counter 1026 is an increment counterinitialized with a counter value of zero, the settle value can be, forexample, the delay value. In the event that the counter value has notyet reached the settle value, the method 1100 returns to block 1104 forthe next pixel value. Otherwise, if the counter value has reached thesettle value, the counter 1026 asserts the compare indicator, therebydirecting the comparator 1016 to compare the voltage V_(BLUE) at theoutput node with the reference voltage V_(REF) at block 1112. If thevoltage V_(BLUE) is less than the reference voltage V_(REF), at block1116 the display detector 120 identifies the display device 1003 asstill connected and the method 1100 returns to block 1102 for the nextdetection cycle. Otherwise, if the voltage reference V_(BLUE) is equalto or greater than the reference voltage V_(REF), at block 1118 thedisplay detector 120 identifies the display device 1003 as disconnectedand at block 1120 the display detector 120 notifies the displaycontroller 112 (e.g., by deasserting the DISPLAY_DET signal or byissuing an interrupt). In an alternate embodiment, the display detector120 could be implemented for each component of the video signal and thedisplay controller 112 therefore could poll each display detector 120 todetermine whether the display device 1003 is disconnected based on theindication from each display detector 120. Further, the displaycontroller 112 may wait until the display device 1003 has been detectedas disconnected for a minimum number of detection cycles beforeidentifying the display device 1003 as disconnected and taking actionaccordingly.

From the above description, it will be appreciated that theimplementation of the display controller 112 of FIG. 10 and its examplemethod 1100 of operation offer a number of advantages. For one, ratherthan requiring an additional current source for purposes of displayconnect/disconnect, the video DAC 1006 (FIG. 10) can be used for displayconnection/disconnection detection purposes in addition to driving thenormal video signals as described above. This implementation also doesnot require additional external logic. Further, by passively monitoringthe voltage output node of the output display interface and comparingthe monitored voltage with a threshold expected to differentiate betweena display connected condition and a display disconnected condition, theimplementation of FIGS. 10 and 11 does not introduce visible artifactsat the display device 1003 because the output to the display device 1003is not altered in implementing the display detection/disconnectionprocess.

FIG. 12 illustrates an example implementation of the display controller112 of FIG. 1 in conjunction with an accessory connector 1216 (oneexample of the output display interface 116 of FIG. 1) for coupling toan accessory device 1203. In one embodiment, the display controller 112is implemented as an integrated circuit comprising a video DAC 1206, anaccessory detector 1206 (corresponding to the device detector 106, FIG.1), and an application processor 1220. The output node of the video DAC1206 is connected to the accessory connector 1216 via a pin 1218 of theintegrated circuit.

The application processor 1220 is configured to process multimedia dataprovided by the video processing device 102 (FIG. 1) and provide thevideo content (VIDEO) for output via the video DAC 1206 via theaccessory connector 1216. In the depicted example, the video content isprovided as a composite signal, such as an NTSC or PAL signal. In otherembodiments, the illustrated technique can be adapted for use with oneor more components of a component-based video signal.

The accessory detector 1206 includes a connect/disconnect detect module1210, a voltage generator 1214, a comparator 1216, an applicationprocessor 1220, a pull-up resistor 1222, and a switch 1224 (alsoidentified herein as “switch 1”). The illustrated implementation furtherincludes a resistor 1226 and a switch 1228 (also identified herein as“switch 2”). The voltage generator 1214 is configured to provide areference voltage V_(REF) configurable by a VCONFIG signal. Thecomparator 1216 includes an input connected to the output (output node)of the video DAC 1206, an input connected to the voltage generator 1214to receive the voltage reference V_(REF) and an output connected to theconnect/disconnect detect module 1210. The resistor 1222 includes afirst terminal connected to a voltage reference V_(DD) and a secondterminal. The switch 1224 includes a first terminal connected to thesecond terminal of the resistor 1222 and a second terminal connected tothe output node of the video DAC 1206, and the switch 1224 is controlledvia a switch signal SW1. The switch 1228 includes a first terminalconnected to the output node via the pin 1218 and a second terminal, andthe switch 1228 is controlled via a switch control signal SW2 providedfrom the display controller 112 via, for example, a general input/outputpin (GPIO) 1230. The resistor 1226 includes a first terminal connectedto the second terminal of the switch 1228 and a second terminalconnected to a ground reference. The connect/disconnect detect module1210 includes an input to receive the output of the comparator 1216, anoutput to provide the switch control signal SW1, an output to providethe switch control signal SW2, and an output to provide a detect signal(DETECT) to the application processor 1220.

In the illustrated example, the accessory connector 1216 is used toconnect any of a variety of accessory devices to the video processingdevice 102 (FIG. 1), including, but not limited to, a display device(e.g., a television or monitor), cable device (e.g., a set top box),headphones, headsets, speakers, and the like. The accessory connector1216 can include a temporarily-connected accessory connector orpermanently-connected accessory connector. However, due to the varietyof accessory devices that can be connected to the accessory connector1216 (or due to the change in impedance of a more permanently attachedaccessory connector 1216 as it is enabled or disabled), it often isadvantageous to determine the accessory class (in terms of impedanceranges) of the accessory device in addition to determining whether anaccessory device has been connected. Accordingly, as described ingreater detail below with reference to FIG. 13, the switches 1224 and1228 can be individually manipulated through a series of detection stepsto determine not only whether the accessory device 1203 has beenconnected, but to determine the accessory class of the accessory device1203 when detected as connected. An accessory class typically can berepresented by a particular impedance or impedance range.

In at least one embodiment, the resistance R₁ of the pull-up resistor1222 is selected to be much larger than the expected resistance R_(A) ofthe accessory device 1203 such that when the switch 1224 is activated(i.e., “closed” or made conductive), the voltage V_(NODE) of the outputnode is pulled to approximately V_(DD) when the accessory device 1203 isnot connected and the voltage VNODE of the output node is pulled toapproximately 0 V (or the ground voltage reference) when the accessorydevice 1203 is connected. To illustrate, assuming that the maximumexpected resistance R_(A) is 8 kΩ, a resistance of at least 15 kΩ forthe resistor 1222 may be sufficient for the voltage V_(NODE) to beidentified as HIGH or a logic “1” when the accessory device 1203 is notconnected (or in a first enable state) and the voltage V_(NODE) to beidentified as LOW or a logic “0” when the accessory device 1203 isconnected (or in a second enable state). Likewise, the resistance of theresistor 1226 can be selected to match the impedance of the intermediateimpedance class of the accessory device 1203.

FIG. 13 illustrates an example method 1300 of operation of theimplementation of FIG. 12 for detecting whether an accessory device hasbeen connected, and if detected as connected, the accessory class of theaccessory device in accordance with at least one embodiment of thepresent disclosure. The method 1300 can represent the operation of thestate machine 200 of FIG. 2 for the state 204.

In the depicted example, it is assumed that the accessory device 1203can belong to three accessory classes: a first accessory class having animpedance of 30Ω or less (e.g., headphones or speakers having impedancesof 8Ω or 16Ω); a second accessory class having an impedance ofapproximately 75Ω (e.g., televisions, monitors, and cable interfaces);and a third accessory class having an impedance of greater than 300Ω(e.g., microphones or headsets). Based on these example impedance rangesof the different accessory classes, the resistance R₂ of the resistor1226 can be selected to be 75Ω so as to match the middle impedancerange. Other resistances can be selected for different impedance rangesas appropriate. Also in this example, it is assumed that the voltagereference V_(DD) is 2.5 V.

At block 1302, the connect/disconnect detect module 1210 initiates theprocess of determining whether the accessory device 1203 is connected byenabling the switch 1224 (switch 1) and disabling the switch 1228(switch 2) via switch control signals SW1 and SW2, respectively.Further, the connect/disconnect detect module 1210 disables the videoDAC 1206, and it is assumed that in the disabled state the video DAC1206 has a relatively high impedance from the viewpoint of the outputnode. In this configuration, the output node is connected to the voltagereference V_(DD) via the resistor 1222. If the accessory device 1203 isconnected, the output node also is connected to ground via theresistance R_(A) of the accessory device 1203. Accordingly, the resistor1222 and the resistance R_(A) operate as a voltage divider such that thevoltage VNODE of the output node can be represented by the followingequation EQ. 1:

$\begin{matrix}{V_{NODE} = {V_{DD} \times \frac{R_{A}}{R_{A} + R_{1}}}} & {{EQ}.\mspace{14mu} 1}\end{matrix}$Thus, in the event that the accessory device 1203 is disconnected, theresistance R_(A) is effectively infinite and thus the voltage V_(NODE)is approximately equal to the voltage reference V_(DD). Assuming thevoltage reference V_(DD) is logic HIGH, V_(NODE)=HIGH in this instance.Otherwise, if the accessory device 1203 is connected and the resistanceR1 is much greater than the resistance R_(A) (i.e., R1>>R_(A)), thevoltage V_(NODE) is approximately equal to ground, or V_(NODE)=LOW(assuming the ground voltage reference is logic LOW).

Accordingly, at block 1304, the connect/disconnect detect module 1210determines whether the voltage V_(NODE) is logic HIGH (near V_(DD)) orlogic LOW (near ground). Alternately, the connect/disconnect detectmodule 1210 can set the voltage generator 1214 to generate a voltagereference V_(REF) between ground and V_(DD) and use the output of thecomparator 1216 to determine whether the voltage V_(NODE) is logic HIGHor logic LOW. In the event that the voltage V_(NODE) is at logic LOW,the connect/disconnect detect module 1210 identifies the accessorydevice 1203 as disconnected and the method 1300 therefore returns toblock 1302 for the next detect cycle. Otherwise, in the vent that thevoltage V_(NODE) is at or near logic HIGH, the connect/disconnect detectmodule 1210 identifies the accessory device 1203 as connected at block1308. Further, the connect/disconnect detect module 1210 can notify theapplication processor 1220 of the detected connection of the accessorydevice 1203 via the DETECT signal or via an interrupt.

Having detected the connection of the accessory device 1203, theconnect/disconnect detect module 1210 initiates the process ofdetermining the accessory class of the accessory device 1203. At block1310, the connect/disconnect detect module 1210 disables the switch 1224(switch 1) and disables the switch 1228 (switch 2) via switch controlsignals SW1 and SW2, respectively. Further, the connect/disconnectdetect module 1210 enables the video DAC 1206, which is assumed to havea resistance R_(DAC) in view of the output node when enabled. At block1312, the connect/disconnect detect module 1210 signals the applicationprocessor 1220 to output a predetermined value to the video DAC 1206 sothat the video DAC 1206 drives a predetermined current I_(TEST) at theoutput node, thereby generating a voltage V_(NODE) at the output node.

In the configuration resulting from the process at block 1310, theeffective resistance R_(NODE) at the output node is represented byequation EQ. 2:R _(NODE) =R _(DAC) ∥R _(A)   EQ. 2Accordingly, the voltage V_(NODE) at the output node resulting from theoutput of the current I_(TEST) at block 1312 is represented by equationEQ. 3:V _(NODE) =I _(TEST) ×R _(NODE) =I _(TEST) ×R _(DAC) ∥R _(A)   EQ. 3If the accessory device 1203 is not connected, EQ. 3 reduces toV_(NODE)=I_(TEST)×R_(DAC).

At block 1314, the connect/disconnect detect module 1210 configures thevoltage generator 1214 to output a specified reference voltage V_(REF)and the comparator 1216 provides a particular output voltage based on acomparison of the voltage V_(NODE) with the voltage V_(REF). In at leastone embodiment, the reference voltage V_(REF) is selected based on thecurrent I_(TEST) and the two highest impedances or impedance rangesexpected for the accessory device 1203 based on the followingrelationship EQ. 4:ITEST×R _(DAC) ∥R _(n-1) ∥R ₂ <V _(REF) <ITEST×R _(DAC) ∥R _(n) ∥R ₂  EQ. 4where R_(n) represents the lowest impedance of the highest expectedimpedance range and R_(n-1) represents the highest impedance of thesecond highest expected impedance range. To illustrate, assuming thatthe current I_(TEST) is 20 mA and the three accessory classes haveimpedance ranges of <30Ω, 75Ω, and >300Ω, and the resistance RDAC is75Ω, the corresponding range is 0.5 V. to 0.66 V (i.e., 20mA*(75Ω∥75Ω∥75Ω) to 20 mA*(75Ω∥75Ω∥300Ω)) and thus the voltage V_(REF)can be selected within this range, for example, V_(REF)=0.55 V.

Accordingly, if the voltage V_(NODE) at the output node resulting fromthe output of the current I_(TEST) is determined to be not greater thanthe voltage V_(REF) at block 1314, the accessory device 1203 isidentified at block 1316 as being in the class of accessories havingimpedances of less than 30Ω, such as headphones or speakers. Theconnect/disconnect detect module 1210 then can provide an indicator ofthe accessory class of <30Ω to the application processor 1220, which mayconfigure its operation and the operation of other components of thevideo processing device 102 accordingly.

Otherwise, if the voltage V_(NODE) is determined to be greater than thevoltage VREF at block 1314, at block 1318 the connect/disconnect detectmodule 1210 disables the switch 1224 (switch 1) and enables the switch1228 (switch 2) via switch control signals SW1 and SW2, respectively. Soconfigured, the connect/disconnect detect module 1210 signals theapplication processor 1220 to provide the predetermined value to thevideo DAC 1206 so as to drive the predetermined current I_(TEST) at theoutput node. At block 1322, the comparator 1216 provides a particularoutput voltage based on a comparison of the resulting voltage V_(NODE)with the voltage V_(REF). In the configuration resulting from theprocess at block 1318, the effective resistance R_(NODE) at the outputnode is represented by equation EQ. 5:R _(NODE) =R _(DAC) ∥R ₂ ∥R _(A)   EQ. 5Accordingly, the voltage V_(NODE) at the output node resulting from theoutput of the current I_(TEST) at block 1320 is represented by equationEQ. 6:V _(NODE) =I _(TEST) ×R _(NODE) =I _(TEST) ×R _(DAC) ∥R ₂ ∥R _(A)   EQ.6If the accessory device 1203 is not connected, EQ. 6 reduces toV_(NODE)=I_(TEST)×R_(DAC)∥R₂. As the impedance range of <30Ω was ruledout at blocks 1314 and 1316, it remains only to determine whether theaccessory device 1203 is in the 75Ω class or >300Ω class. Using theexample values above, if the accessory device 1203 is in the 75Ω class,the voltage V_(NODE) at block 1322 would be approximately 0.5 V (i.e.,20 mA×75Ω∥75Ω∥75Ω), which is less than the voltage V_(REF) of 0.57 V.Conversely, if the accessory device 1203 is in the >300Ω class, thevoltage V_(NODE) at block 1322 would be greater than 0.66 V (i.e., 20mA×75Ω∥75Ω∥300Ω), which is greater than the voltage reference V_(REF) of0.57 V. Accordingly, if the voltage V_(NODE) is identified as notgreater than the voltage V_(REF) by the comparator 1216, the activedetect module 1210 identifies the accessory device 1203 as belonging toclass of accessory devices having impedances of approximately 75Ω atblock 1324 and signals this identification to the application processor1220 so that the video processing device 102 (FIG. 1) can be configuredaccordingly. Otherwise, if the voltage V_(NODE) is identified as greaterthan the voltage V_(REF) by the comparator 1216, the active detectmodule 1210 identifies the accessory device 1203 as belonging to classof accessory devices having impedances of >300Ω at block 1326 andsignals this identification to the application processor 1220 so thatthe video processing device 102 (FIG. 1) can be configured accordingly.

Although FIGS. 12 and 13 illustrate an example implementation fordetermining which of three different impedance ranges an connectedaccessory belongs, the technique of FIGS. 12 and 13 can be adapted todetermine more than three impedance ranges in accordance with at leastone embodiment of the present disclosure. To illustrate, a plurality ofresistors and switches can be used to selectively couple the output nodeto the ground voltage reference so as to generate different effectiveresistances at the output node. The voltage resulting from theapplication of the known current I_(TEST) to the different effectiveresistances then can be used to determine which impedance class of fouror more impedance classes applies to the connected accessory device.

In addition to hardware implementations of devices that are adapted tosurvive perform the functionality in accordance with one of theembodiments of the present invention, such devices may also be embodiedin software disposed, for example, in a computer usable (e.g., readable)medium configured to store the software (e.g., a computer readableprogram code). The program code causes the enablement of embodiments ofthe present invention, including the following embodiments: (i) thefunctions of the systems and methods disclosed herein (such as systemsand methods detecting display and/or accessory connection and/oraccessory class); (ii) the fabrication of the systems and methodsdisclosed herein (such as the fabrication of devices that are enabled todetect display and/or accessory connection and/or accessory class); or(iii) a combination of the functions and fabrication of the systems andmethods disclosed herein.

For example, this can be accomplished through the use of generalprogramming languages (such as C or C++), hardware description languages(HDL) including Verilog, Verilog-A, HDL, VHDL, Altera HDL (AHDL) and soon, or other available programming and/or schematic capture tools (suchas circuit capture tools). The program code can be disposed in any knowncomputer usable medium including semiconductor, magnetic disk, opticaldisk (such as CD-ROM, DVD-ROM) and as a computer data signal embodied ina computer usable (e.g., readable) transmission medium (such as adigital, optical, or analog-based medium). It is understood that thefunctions accomplished and/or structure provided by the systems andtechniques described above can be represented in a core (such as a GPUcore) that is embodied in program code and may be transformed tohardware as part of the production of integrated circuits via synthesisof the hardware description language-based software representation.

In this document, relational terms such as “first” and “second”, and thelike, may be used solely to distinguish one entity or action fromanother entity or action without necessarily requiring or implying anyactual such relationship or order between such entities or actions. Theterms “comprises”, “comprising”, or any other variation thereof, areintended to cover a non-exclusive inclusion, such that a process,method, article, or apparatus that comprises a list of elements does notinclude only those elements but may include other elements not expresslylisted or inherent to such process, method, article, or apparatus. Theterm “another”, as used herein, is defined as at least a second or more.The terms “including”, “having”, or any variation thereof, as usedherein, are defined as comprising. The term “coupled”, as used hereinwith reference to electro-optical technology, is defined as connected,although not necessarily directly, and not necessarily mechanically.

Other embodiments, uses, and advantages of the disclosure will beapparent to those skilled in the art from consideration of thespecification and practice of the disclosure disclosed herein. Thespecification and drawings should be considered exemplary only, and thescope of the disclosure is accordingly intended to be limited only bythe following claims and equivalents thereof.

What is claimed is:
 1. A method comprising: providing a video signal fortransmission via an output node of a display interface of a videoprocessing device, the display interface coupleable to a display deviceand the video signal comprising an active segment comprising imageinformation and an inactive segment comprising synchronizationinformation, wherein providing the video signal comprises: providing apredetermined first current to the output node during transmission ofboth the active segment and the inactive segment, the display devicebeing configured to latch the first current as a reference black levelduring the inactive segment; and providing a second currentrepresentative of the active segment to the output node duringtransmission of the active segment, wherein a total current provided tothe output node during transmission of the active segment is equal to asum of the first current and the second current; and determining whetherthe display device is coupled to the display interface based on acomparison of a first voltage at the output node during transmission ofan inactive component of the inactive segment via the output node to areference voltage, the first voltage generated at the output node inresponse to providing the first current to the output node.
 2. Themethod of claim 1, further comprising: configuring the video processingdevice into a low power mode in response to determining that a displaydevice is not connected to the display interface based on the comparisonof the first voltage to the reference voltage.
 3. A video processingdevice comprising: a display interface coupleable to a display device; adisplay controller configured to transmit a video signal via an outputnode of the display interface, the video signal comprising an activesegment comprising video information and an inactive segment comprisingsynchronization information, wherein the display interface is configuredto provide the video signal by: providing a predetermined first currentto the output node during transmission of both the active segment andthe inactive segment, the display device being configured to latch thefirst current as a reference black level during the inactive segment;and providing a second current representative of the active segment tothe output node during transmission of the active segment, wherein atotal current provided to the output node during transmission of theactive segment is equal to a sum of the first current and the secondcurrent; and a display detector configured to determine whether thedisplay device is coupled to the display interface based on a comparisonof a first voltage at the output node during transmission of theinactive segment to a reference voltage, the first voltage generated atthe output node in response to the provision of the first current to theoutput node.
 4. The video processing device of claim 3, wherein thedisplay interface is compatible with a display interface selected from agroup consisting of: a Red-Green-Blue (RGB) interface; a composite videointerface; a component video interface; and an S-video interface.
 5. Thevideo processing device of claim 3, wherein the inactive segmentcomprises one selected from a group consisting of: a horizontalsynchronization component; and a vertical synchronization component. 6.The video processing device of claim 3, further comprising: a controllerto configure the video processing device into a low power mode inresponse to determining that a display device is not connected to thedisplay interface based on the comparison of the first voltage to thereference voltage.
 7. A method comprising: converting, at a videoprocessing device, a series of pixel values to a corresponding outputcurrent; providing the output current to an output node of a displayinterface of the video processing device for transmission, a voltage ofthe output node varying with the output current; for each pixel value ofthe series of pixel values: comparing the pixel value with a thresholdvalue; adjusting a count value in response to determining the pixelvalue is at least as great as the threshold value; and resetting thecount value in response to determining the pixel value is less than thethreshold value; and responsive to the count value reaching apredetermined settling value, determining whether a display device hasbeen disconnected from the display interface based on a comparison of areference voltage to the voltage at the output node.
 8. The method ofclaim 7, wherein the series of pixel values comprises pixel values of acomponent of a video signal, the component comprising one of a groupselected from: a color component; a luminance component; or achrominance component.
 9. The method of claim 7, further comprising:configuring the video processing device into a low power mode inresponse to determining that the display device has been disconnectedfrom the display interface based on the comparison of the referencevoltage to the voltage at the output node.
 10. The method of claim 7,wherein: the output current has a maximum current, wherein the voltageat the output node for the maximum current is a first voltage when thedisplay device is connected and is a second voltage when the displaydevice is not connected, the second voltage greater than the firstvoltage; the threshold value corresponds to a first output current,wherein the voltage at the output node for the first current is a thirdvoltage when the display device is connected and is a fourth voltagewhen the display device is not connected, the third voltage less thanthe first voltage and the fourth voltage greater than the first voltageand less than the reference voltage; and the reference voltage isgreater than the first voltage and less than the fourth voltage.
 11. Avideo processing device comprising: a display interface coupleable to adisplay device; a video digital-to-analog converter (DAC) to convert aseries of pixel values to a corresponding output current and to providethe output current to an output node of the display interface fortransmission, a voltage of the output node varying with the outputcurrent; a digital comparator comprising an input to receive the seriesof pixel values, an input to receive a threshold value, and an output,wherein the digital comparator is to, for each pixel value of the seriesof pixel values, provide a first value in response to determining thepixel value meets or exceeds the threshold value and provide a secondvalue in response to determining the pixel value is less than thethreshold value; a counter comprising an input connected to the outputof the digital comparator and an output, wherein the counter is to:adjust a count value in response to receiving the first value at theinput; reset the count value in response to receiving the second valueat the input; and provide a compare indicator at the output in responseto the count value reaching a predetermined settling value; a voltagecomparator to compare a reference voltage to the voltage at the outputnode in response to the compare indicator; and a disconnect detectmodule to determine whether a display device has been disconnected fromthe display interface based on an output of the comparator in responseto the compare indicator.
 12. The video processing device of claim 11,wherein the disconnect detect module further is to configure the videoprocessing device into a low power mode in response to determining thatthe display device has been disconnected from the display interfacebased on the output of the comparator.
 13. The video processing deviceof claim 11, wherein: the video DAC has a maximum current, wherein thevoltage at the output node for the maximum current is a first voltagewhen the display device is connected and is a reference voltage when thedisplay device is not connected, the reference voltage greater than thefirst voltage; the threshold value corresponds to a first outputcurrent, wherein the voltage at the output node for the first current isa third voltage when the display device is connected and is a fourthvoltage when the display device is not connected, the third voltage lessthan the first voltage and the fourth voltage greater than the firstvoltage and less than the second voltage; and the reference voltage isgreater than the first voltage and less than the fourth voltage.
 14. Atangible computer readable medium storing instructions which areoperable upon by a computer system to manipulate the computer system toperform a portion of a process to fabricate a device, the devicecomprising: a display interface coupleable to a display device; a videodigital-to-analog converter (DAC) to convert a series of pixel values toa corresponding output current and to provide the output current to anoutput node of the display interface for transmission, a voltage of theoutput node varying with the output current; a digital comparatorcomprising an input to receive the series of pixel values, an input toreceive a threshold value, and an output, wherein the digital comparatoris to, for each pixel value of the series of pixel values, provide afirst value in response to determining the pixel value meets or exceedsthe threshold value and provide a second value in response todetermining the pixel value is less than the threshold value; a countercomprising an input connected to the output of the digital comparatorand an output, wherein the counter is to: adjust a count value inresponse to receiving the first value at the input; reset the countvalue in response to receiving the second value at the input; andprovide the compare indicator at the output in response to the countvalue reaching a predetermined settling value; a voltage comparator tocompare a reference voltage to the voltage at the output node inresponse to the compare indicator; and a disconnect detect module todetermine whether a display device has been disconnected from thedisplay interface based on an output of the comparator in response tothe compare indicator.
 15. The tangible computer readable medium ofclaim 14, wherein the disconnect detect module further is to configurethe device into a low power mode in response to determining that thedisplay device has been disconnected from the display interface based onthe output of the comparator.
 16. The tangible computer readable mediumof claim 14, wherein: the video DAC has a maximum current, wherein thevoltage at the output node for the maximum current is a first voltagewhen the display device is connected and is a second voltage when thedisplay device is not connected, the second voltage greater than thefirst voltage; the threshold value corresponds to a first outputcurrent, wherein the voltage at the output node for the first current isa third voltage when the display device is connected and is a fourthvoltage when the display device is not connected, the third voltage lessthan the first voltage and the fourth voltage greater than the firstvoltage and less than the reference voltage; and the reference voltageis greater than the first voltage and less than the fourth voltage. 17.The tangible computer readable medium of claim 14, wherein theinstructions comprise register transfer level (RTL) instructionsconfigured to determine a design of the device.